Extension of truncated CT images for use with emission tomography in multimodality medical images

Abstract

An apparatus and method for expanding the FOV of a truncated computed tomography (CT) scan. An iterative calculation is performed on the original CT image to produce an estimate of the image. The calculated estimate of the reconstructed image includes the original image center and a estimate of the truncated portion outside the image center. The calculation uses an image mask with the image center as one boundary.

Description

CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM FOR PRIORITY[0001]This application is a continuation-in-part of copending U.S. application Ser. No. 11 / 428,456, filed Jul. 3, 2006, which claimed priority under 35 U.S.C. §119(e) of Provisional Application Ser. No. 60 / 696,307 filed Jul. 1, 2005.BACKGROUND OF THE INVENTION[0002]1. Technical Field[0003]The present invention relates generally to medical diagnostic imaging and to use of medical images in one imaging modality with medical images from another imaging modality. More specifically the invention relates to extension or extrapolation of image data from a Computed Tomography (CT) transmission scan having a limited Field of View (FOV) so as to extend the CT image to a larger FOV. The FOV extension increases the anatomic information provided by the CT scan, and it makes the attenuation data provided by the CT image more accurate for correcting radionuclide emission data obtained from an emission computed tomography scan such as Pos...

AI Technical Summary

Benefits of technology

[0027]In another embodiment of the present invention, the mask used in the process described herein is reduced in area. The truncated mask excludes additional areas from CT image extension such as the region below the lowest point of the reconstructed object and the region above the highest point of the reconstructed object in the FOV. In yet another embodiment of the present invention, the method for extending the FOV can be improved if the CT system is part of a combined PET / CT scanner or SPECT / CT scanner. In this embodiment, the outer boundary of the mask is determined from SPECT or PET images whose axial positions corresponding to those of the CT images. This invention reduces the computation time for the extension of the CT image FOV and improves the accuracy with respect to the prior art of CT images in the region of extension. The improved CT images, in turn, improve the accuracy of the PET and SPECT attenuation correction with respect to the prior art.

Problems solved by technology

However, with the exception of the brain, the co-alignment of images from different modalities is not straightforward or very accurate, even when surface markers or reference points are used.

However, iterative methods are generally more computationally intensive and more time-consuming than non-iterative methods.

Consequently, in the past iterative techniques were not used in CT as sufficient computational power was cost prohibitive for the resolution and contrast requirements of that modality.

According to U.S. Pat. No. 5,376,795, photon attenuation constitutes a major deficiency in diagnosis of heart disease with SPECT and is a major source of error in the measurement of tumor metabolism using radionuclide techniques.

One limitation of attenuation maps created by CT transmission data is the relatively small usable FOV (typically on the order of 50 cm diameter) compared to the FOV of a PET scanner (typically on the order of 70 cm diameter or more).

However, for various reasons, these attempts either do not extend the FOV far enough or introduce artifacts and / or distortion in the images.

However, these prior art methods have proven unacceptable for reconstructing truncated views.

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